Along with a recent growing interest in environmental issues, move to paperless offices has rapidly been promoted. For this purpose, there is conventionally known a document management system which reads paper documents accumulated in binders by using a scanner, converts the read images into portable document format (to be abbreviated as “PDF” hereinafter) data, and accumulates them in an image storage device as a database.
Under these circumstances, even a forbidden document can sometimes easily be copied and carried out. To know when information that should not be printed has been printed and who has printed it, a method of saving an input image as image data is known (e.g., Japanese Patent Laid-Open No. 6-270477).
Another method is also known in which input image data is compared with a predetermined image, thereby determining whether the data is information which should not be printed (e.g., Japanese Patent Laid-Open No. 6-178066).
However, the former method requires an image storage area with an enormous capacity to accumulate image data each having a large data amount in the image processing system. The latter method can cope with a change in various directions. However, to inhibit printing of data matching a given keyword, patterns corresponding to various volumes and sizes must be generated in correspondence with the same keyword, resulting in a cumbersome determination process.